1. Field of the Invention
The present invention relates to a photographic silver halide photosensitive material. More particularly, the present invention relates to a silver halide color photographic photosensitive material which is useful for the improvement of an image forming technique for high-temperature processing of tabular silver chloride grains or silver halide grains composed of silver chlorobromide, silver chloroiodide or silver chloroiodobromide having a high content of silver chloride.
2. Description of the Related Art
Owing to remarkable development of color photographic photosensitive materials utilizing silver halides, high-quality color images are now easily available. For example, according to so-called ordinary color photography, color prints are obtained by taking a photograph utilizing a color negative film, processing the film, and optically printing the image information which is recorded in the processed color negative film onto color photographic printing paper. Recently, this process has made remarkable progress, and large-scale, centralized color laboratories, in which a large quantity of color prints are produced efficiently, and the so-called mini-labs which are installed in shops and are designed to use compact and simple printer-processors have spread widely. Therefore, anybody can enjoy color photography easily.
The color photography, now in common use, reproduces color by the subtractive color process. Generally, a color negative film comprises a transparent support and photosensitive layers thereon utilizing silver halide emulsions as photosensitive elements sensitive to blue, green or red wavelength regions respectively, and so-called color couplers capable of producing a yellow, magenta or cyan dye having a complementary hue of the sensitive wavelength region of each photosensitive layer. A color negative film exposed during photography, is processed in a color developing solution containing an aromatic primary amine developing agent. At this time, the developing agent develops, i.e., reduces the exposed silver halide grains, and the oxidized form of the developing agent, which is formed concurrently with the foregoing reduction, undergoes a coupling reaction with the color coupler to form dyes. The metal silvers (developed silver) generated by the development and the unreacted silver halides are removed through a bleaching and fixing process, respectively. This creates a color image on the color negative film. Subsequently, color photographic printing paper, which comprises a reflective support and photosensitive layers coated thereon having a combination of photosensitive wavelength regions and hue in each layer, similar to the color negative film, is optically exposed to light through the processed color negative film, and is then subjected to the color developing, bleaching and fixing processes as in the case of the negative film to obtain a color print having a color image composed of dye images so that an original image can be reproduced.
Although these systems are widely adopted at the present time, there is a growing demand for a simpler system. The first reason for this is that expertise and skilled operation are necessary due to the requirement of strict control of the composition and the temperature of the solutions in processing baths for the above-mentioned procedure consisting of color development, bleaching and fixation. The second reason for this is that equipment to be used exclusively for the developing process is often required, due to substances, such as developing agents and bleaching agents comprising an iron chelate compound, the discharge of which is regulated from the standpoint of environmental protection. The third reason for this is that the currently available systems do not satisfactorily fulfill the requirement for rapid reproduction of recorded images. The above-mentioned processes still take time, although this time has been shortened with recent advances in technology.
Based on this background, many improved techniques have been proposed. In particular, in order to make the developing process simple and rapid, a variety of techniques have been proposed which use silver halide grains having a higher silver chloride content (50% or more and hereinafter referred to as "silver chloride rich grains"). The use of silver chloride rich grains brings about the advantages, for example, that the processing speed increases and the reusability of the processing solutions are improved.
Consequently, in recent years, most photosensitive materials for printing, such as color photographic printing paper, use silver chloride rich grains. Under ordinary manufacturing conditions, the produced silver chloride rich grains tend to be grains in which (100) planes constitute the exterior faces of the grains (hereinafter referred to as (100) grains) The grains actually used in practice have been cubes. Recently, tabular (100) grains, having larger specific surface areas (the ratio of the surface area to the volume) with the advantages that spectral sensitization can be effectively performed and the covering power after the developing process is enhanced, have also been developed. Examples of these tabular (100) grains are disclosed in, e.g., U.S. Pat. Nos. 5,320,938, 5,264,337 and 5,292,632.
However, in the case of the photosensitive materials using the silver chloride rich grains, the development characteristics of the silver chloride rich grains cause various problems. The first problem is that it is difficult to obtain a highly sensitive photographic response at an early stage of developing process, because the high-speed development of the individual grains of the silver halide emulsion containing the silver chloride rich grains often causes the timing of the start of the development of the light-exposed grains to vary. The second problem is that any attempt to utilize the high developing capability of the silver chloride rich grains is often associated with deterioration of the graininess. Consequently, it is very difficult to fulfill the characteristics of photosensitive materials for photographing such as a wide exposure latitude and superior level of graininess by use of a silver halide emulsion composed of the silver chloride rich grains. Since these problems still remain unsolved, many fundamental problems need to be solved before the photosensitive materials for photographing using silver halide emulsions composed of silver chloride rich grains can be put to practical use. The third problem is that the silver chloride rich grains in which (100) planes constitute the exterior faces of the grains tend to cause more fogging in comparison with conventional silver bromide grains.
As an effective solution to the above-described problems, a method has been proposed recently which comprises releasing or producing diffusive dyes on an image by means of thermal development and transferring the diffusive dyes to a dye-fixing element.
According to this method, it is possible to obtain negative or positive color images by selecting the kind of dye-donating compound or silver halide to be used. The details are described in, e.g., U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,137 and 4,559,290, Japanese Patent Application Laid-Open (JP-A) Nos. 58-149,046, 59-218,443, 60-133,449 and 61-238,056, European Patent Application Laid-Open Nos. 220,746A2 and 210,660A2, and Journal of Technical Disclosure No. 87-6,199.
In another attempt to fulfill the above-mentioned requirements, a technique has been reported which will lessen the load on the environment and contribute to the simplification of the system by establishing a color image formation system without the use of the color developing agents or bleaching agents now in use in current systems. For example, IS & T's 48th Annual Conference Proceedings, p. 180, discloses a system in which the dye formed in the developing reaction is transferred to a mordant layer and thereafter a photosensitive material is stripped to remove the developed silver and unreacted silver halide from an image formed by the dye without the use of a bleach-fixing bath which has been indispensable to conventional color photographic processing. However, this technique cannot perfectly solve environmental problems because a developing process using a processing bath containing a developing agent is still necessary.
Fuji Photo Film Co., Ltd. has proposed Pictrography and Pictrostat systems which dispense with a processing solution containing a developing agent. In these systems, a small amount of water is supplied to a photosensitive material containing a base precursor, and then the photosensitive material and an image receiving material are placed face to face and heated to promote the developing reaction. This system does not use the aforementioned processing bath and, in this regard, is advantageous with respect to environmental protection. However, since this system is used in the application where the formed dye is fixed in the dye fixing layer which is then appreciated in the form of color images, there has been a demand for a system usable as a recording material for photographing.
The present inventors have conducted studies to establish a method wherein a photosensitive material is used as a recording material for photographing without undergoing a fixing treatment, thereby enabling easy and rapid processing without the use of processing solutions or with use of a minimum amount of processing solutions. As a result, they found that quickening of the process is possible by, e.g., using silver chloride rich grains. But this speed up makes the image quality insufficient because of a drop in the maximum density. As a solution to this problem, they have found a method wherein a photosensitive material comprises a coupler having a specific structure and a silver halide emulsion containing silver chloride rich, tabular grains whose exterior faces are made mainly of (100) and (111) planes.
Further, they have studied a photosensitive material for photographing having the graininess improved by use of silver chloride in the heat development system.
In the heat development system, however, in which the processing is performed at a high temperature, the tendency of the (100) grains to fog is greater than it is in conventional systems. Another type of silver chloride grains are grains having (111) planes as exterior faces (hereinafter referred to as (111) grains).
Meanwhile, specifications including U.S. Pat. Nos. 5,264,337, 5,292,632 and 5,310,635 and WO94/22,054 disclose the use of an emulsion containing tabular, silver chloride rich grains having (100) planes as the exterior faces of the grain to a photosensitive material for photographing. Owing to the use of an emulsion rich in silver chloride, this technique provides the advantages that a high-speed developing process is possible and that the same processing solution can be used for the photosensitive material for photographing and the photosensitive material for print. However, no mention is made of the introduction of a coupler having a specific structure to the photosensitive material in the above-mentioned specifications.
According to Japanese Patent Application Publication (JP-B) No. 7-120,014, fogging can be diminished, while high sensitivity is maintained in a photosensitive material for heat development, through the use of (100) silver halide grains having three sides in such a relationship that the length of one side is 2 or more times, or otherwise 0.5 or less times, the arithmetic mean of the other two sides. However, the image quality obtained through these methods is still unsatisfactory, especially with respect to the maximum density.
The tabular, silver chloride grains having (100) planes are described in many other reports, examples of which include U.S. Pat. No. 5,314,798, EPNos. 534,395A, 617,321A, 617,317A, 617,318A, 617,325A, WO94/22,051, EP No. 616,255A, U.S. Pat. Nos. 5,356,764, 5,320,938 and 5,275,930.
Also, tabular grains whose exterior faces are made mainly of (111) planes are described in a variety of reports, examples of which include U.S. Pat. No. 4,439,520, and U.S. Pat. No. 5,250,403 which discloses so-called extremely thin tabular grains having an equivalent-circle diameter of 0.7 .mu.m or more and a thickness of 0.07 .mu.m or less. U.S. Pat. No. 4,435,501 discloses a technique whereby a silver salt is grown epitaxially on the surface of tabular grains. Further, there have been disclosed many inventions recently for the purpose of improving the performance of the tabular grains in, for example, EP Nos. 0,699,947A, 0,699,951A, 0,699,945A, 0,701,164A, 0,699,944A, 0,701,165A, 0,699,948A, 0,699,946A, 0,699,949A and 0,699,950A. These disclosures relate to silver bromide and silver iodobromide, but there is no description of silver halide containing silver chloride grains having (111) planes as exterior faces.
Special techniques are required for the preparation of (111) grains rich in silver chloride. For example, U.S. Pat. No. 4,399,215 issued to Wey discloses a method for the preparation of tabular, silver chloride rich grains by use of ammonia. This method, however, is associated with difficulty in obtaining small-sized grains which are useful in practice. This is because the use of ammonia increases the solubility of the already highly soluble silver chloride grains. Another disadvantage of this method is increased fogging due to high pH values of 8 to 10 at the time of preparation.
On the other hand, U.S. Pat. No. 5,061,617 issued to Maskasky discloses silver chloride rich (111) grains prepared by the use of a thiocyanate. Like ammonia, thiocyanate increases the solubility of silver chloride.
It has been known to add a crystal habit controlling agent at the time of grain formation as a method that enables the exterior faces of silver chloride rich grains to be made up of a (111) plane. Examples of these methods are shown below.
Crystal habit Patent(Publication) No. controlling agent Inventor US4400463 azaindenes + thioether Maskasky peptizer US4783398 2-4-dithiazolydinone Mifune et al. US4713323 aminopyrazolopyrimidine Maskasky US4983508 bispyridinium salt Ishiguro et al. US5185239 triaminopyrimidine Maskasky US5178997 7-azodindole compound Maskasky U55178998 xanthine Maskasky JP-A No. 64-70741 dye Nishikawa et al. JP-A No. 3-212639 aminothioether Ishiguro JP-A No. 4-283742 thiourea derivative lshiguro JP-A No. 4-335632 triazolinium salt Ishiguro JP-A No. 7-146891 monopyridinium salt Oozeki et al.
Despite the above-described technical developments, there is still the demand for an emulsion having a still higher level of sensitivity and little fogging as a preferable emulsion for use in photosensitive material for photographing in particular.
Meanwhile, the couplers having the structure useful in the present invention are disclosed in, for example, U.S. Pat. Nos. 3,725,067, 4,500,630 and 4,540,654. However, these patents make no mention of the effect of these couplers in a silver halide color photographic photosensitive material in which a color image is formed by placing the photosensitive layer of a photosensitive material and the processing layer of a processing material face to face and by heating both materials. And, these patents make absolutely no mention of the effect of these couplers in a color photosensitive material for heat development having at least one photosensitive layer comprised of an emulsion comprising tabular silver halide grains having a silver chloride content of 50 mol % or more (1) wherein the tabular silver halide grains, which have major exterior faces made up of a (100) plane and a plane of projection of the grain in the shape of a rectangle of a length to width ratio ranging from 1:1 to 1:2 to give an aspect ratio of 2 or greater, account for 50% or more of the total projected area of the silver halide grains of the emulsion, or (2) wherein the tabular silver halide grains, which have major exterior faces made up of a (111) plane and a plane of projection of the grain in the shape of a hexagon with the ratio of the lengths of neighboring sides ranging from 1:1 to 1:10 to give an aspect ratio of 2 or greater, account for 50% or more of the total projected area of the silver halide grains of the emulsion.